The present invention relates generally to hydraulic control valves, and more specifically to a hydraulic control valve for activating a double-acting hydraulic cylinder on a tractor or similar vehicle.
Hydraulic circuits, particularly on farm tractors, are known to feature at least one control valve operated manually by the user to regulate the flow of pressurised hydraulic fluid to and from a double-acting cylinder. Control valves of this sort are often xe2x80x9cpackedxe2x80x9d together to form a control valve assembly, supplied from the same pressurised fluid source, and can activate different user devices separately as required by the operator. For example, a typical control valve assembly comprises one or a number of stacked valves enclosed by two end plates; the hydraulic valves and end plates forming the pack are held together in a fluid-tight manner by bolts having threaded ends to which respective nuts are attached. Normally, each valve has a manually operated lever mechanism designed to move a spool in two opposite directions defined by the longitudinal axis of the spool so as to open and close conduits hydraulically connected to the user device. In some embodiments, the spool, at least along a portion of its line of travel, may activate at least one non-return valve by cam means forming part of the spool, and between which the spool may comprise two flat faces for increasing outflow of the pressurised fluid to and from the user device.
It is therefore essential that, during its travel the spool be prevented from rotating unintentionally about its longitudinal axis, in which case, the cam means would be unable to act on the stem of the non-return valve, on account of one of the two flat facesxe2x80x94which does not constitute a valid ramp for opening the non-return valvexe2x80x94being positioned facing the end of the spring-loaded valve stem. As this would result in jamming of the control valve, prior art control valves use lever mechanisms that provide for both moving and preventing unintentional rotation of the spool.
In actual use, however, such lever mechanisms have proved fairly bulky, and can only be operated by a lever close to the valve itself.
Accordingly, it is an object of the present invention to eliminate the lever mechanism activating the spool of a hydraulic valve, and to adopt instead a cable actuator, in particular a Bowden cable, that substantially comprises a wire enclosed inside a casing in which the wire can slide when pulled or pushed by the operator.
Another object of the present invention is to provide a novel control valve that may be remotely operated, e.g. from the driver""s seat of a tractor.
These and other objects, features and advantages are accomplished according to the instant invention by providing a hydraulic control valve comprising a main body in which is formed a pressurised-fluid inlet opening; first and second conduits in fluid flow communication with a user device; and at least one spool for regulating pressurised fluid flow to and from the user device. The spool has a longitudinal axis, and the position of the spool is regulated by an actuating device, the hydraulic valve being characterised in that the actuating device comprises guide means for preventing the spool from rotating about its axis. The actuating device comprises wire means for moving the spool in two opposite directions defined by its longitudinal axis.